It is known to design the longitudinal side edges of floorboards with all sorts of mutually engaging configurations to enable the floorboards to be laid tight together in interlocking arrangement without the boards needing to be glued or nailed. One side edge configuration normally has a tongue or tenon, which is designed to lockingly engage in a groove or notch in the opposing side edge of an adjacent floorboard. The short-side or end-side edges can also be provided with mutually engaging tongues and grooves. These glue-free and nail-free laying systems of the “snap-in type” generally work very well for the creation of so-called floating laminated parquet floors.
In the laying of floor heating systems in combination with such floors, loops of electric floor heating cables or hot water pipes are usually first laid in or on the sub-floor, before the floorboards are laid on top of these with, inter alia, an intermediate, tread-damping layer. This implies a large-scale laying exercise and an increased structural height of the floor.
Floorboards having integrated grooves for laying of electric cables for floor heating have also been proposed; see, for example, GB 888,842 and WO 2006/039726. In these solutions, the electric cable can be laid in a groove within the thickness of the boards at the actual joint between adjacent floorboards, so that the structural height has no need to be increased. However, the laying of the heating cable in a milled-out groove implies a less good distribution and spreading of the heat in the floor, the heat emission instead being concentrated onto the actual groove region, with increased risk of drying-out and cracking.
Another peculiarity which characterizes existing floorboards, regardless of whether or not they have integrated grooves for the laying of heating cables, is that the opposite longitudinal side edges of each board must be designed with different, complementary engagement profiles, which means that a board can only be laid with its one side against a previously laid board.
WO 2006/136412 A1 and EP 1 585 875 B1 describe floor laying systems in which a profiled rail which couples together the boards is designed with a hollow, asymmetrical profile corresponding to the asymmetrical profile of the board, so that the profiled rail forms a board-like bridge element between the boards, in which electric cables, for example, can be laid. The side grooves in the respective neighbouring boards have no crosswise diagonally opposing beveled faces, nor do they have a slot opening into each groove, which slot runs substantially parallel with the top and bottom sides of the board and forms with the bottom side in each opposing board a resilient tongue that presses the profiled rail with a substantially constant pressure against a diagonally opposing beveled face in the opposing board. This can give rise to a risk of gaps being formed, which are caused, above all, by changes in humidity and temperature. In order to avoid this risk of gaps, a resilient interaction between the integral components is required, which offers the chance of humidity and temperature related expansion and shrinkage movements of the boards, with maintained cohesion between the same. The profiled rails in the just named WO and EP publications are also without flanges which are essential to the coupling and diverge towards the top side of the boards and which engage in corresponding recesses in each groove.